1. Field of the Invention
The present invention relates to a moisture sensor having a polymer film, which detects variation of humidity in the atmosphere with a variation in the impedance of the polymer film.
2. Description of the Prior Art
As a moisture sensor wherein an impedance varies depending upon a variation of humidity in the atmosphere, there have been, for example, a moisture sensor having a sintered body of metal oxides such as tin oxide(SnO.sub.2), or a metal oxide film; a moisture sensor having a hydrophilic polymer film; a moisture sensor having an electrolyte salt such as lithium chloride(LiCl); and a moisture sensor having a hygroscopic resin or polymer film in which conductive particles or fibers such as carbon are dispersed.
While a moisture sensor containing a metal oxide film or a hydrophilic film has a wide moisture-sensitivity range, its resistance varies exponentially responding to relative humidity in the atmosphere. A moisture sensor having an electrolyte salt such as lithium chloride detects only humidity in a narrow range so that when it is allowed to stand in a high humidity atmosphere for a long period of time, the electrolyte salt therein is eluted or diluted resulting in deterioration of the moisture sensitive characteristic of the sensor, and accordingly it cannot be used for determination of high humidity. Also, a moisture sensor having a hygroscopic resin or the like, in which conductive particles or fibers are dispersed, cannot detect a humidity in a wide range because it exhibits a steep variation of the resistance thereof in a high humidity atmosphere, while it is not sensitive to low humidity.